i'm pretty sure this would be impossible, since how would your emails be encrypted in your pm mailbox? which public key is pm supposed to use to encrypt the stored copy? the address doesn't actually exist if you use an external smtp to send from it, so protonmail can't store keys for it.
i'm pretty sure this would be impossible, since how would your emails be encrypted in your pm mailbox? which public key is pm supposed to use to encrypt the stored copy? the address doesn't actually exist if you use an external smtp to send from it, so protonmail can't store keys for it.
this one seems like a non-starter